(a) Field of the Invention
This invention relates to a method for the preparation of low molecular weight alkoxylated amino resins, generally used as cross-linking agents in the preparation of surface coatings and the like.
(b) Description of the Prior Art
At present, there are two routes to the preparation of these alkoxylated resins, which depend on the use of solutions of formaldehyde. In one route, aqueous formaldehyde is used. This presents the twin problems that since water removal from the resin is expensive, it is desirable to use a concentrated formaldehyde solution. But such solutions are relatively unstable and thus are difficult to handle. In a second route, an alcoholic solution of formaldehyde is used. This has the disadvantage that such solutions although far more stable than aqueous ones, are also far more expensive.
Attempts to prepare alkoxylated resins by reaction of the formaldehyde and amino compound with an alcohol have not proven very successful. The presence of the water from the formaldehyde solution hinders the etherification of the methylol groups. This hindering results in a higher than desired level of polymerization. Further, this water has to be removed, generally again by an expensive evaporation procedure involving heat and/or vacuum. The resulting alkoxylated amino resins have impaired properties, such as high viscosity and lowered mineral spirits tolerance, when compared to similar resins prepared from alcoholic formaldehyde solutions.